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In reactive ion etching (RIE) processes of vertical metal oxide semiconductor (MOS) devices, damages caused by ion bombardment at oblique incidence may affect the device performance. In this study, damage formation on Si surfaces by energetic hydrogen and halogen ions has been examined for different angles of incidence with the use of a multi-beam system. The beam experiments and molecular dynamics simulations have shown that the depth of a Si damage layer caused by H þ ion injections has weak dependence on the angle of incidence. It is also found experimentally that the Cl þ or Br þ ion etching yield of a Si substrate that is damaged by energetic hydrogen ions prior to Cl þ or Br þ ion injections is essentially the same as that of the undamaged Si substrate. The results indicate that, in the etching process of vertical MOS gate structures, surface bombardment by energetic hydrogen ions even at oblique incidence may cause several-nanometer deep damages to the Si channels but etching yields for the gate fabrication are unlikely to be altered by the surface damages. #

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During gate etching processes of multigate fin-type field effect transistors (finFETs), energetic ions may hit the vertical walls at grazing angles and form damaged layers there. Such damages, if formed, can affect the device performance since part of the Si vertical walls of a finFET structure is used as a conductive channel. In this article, possible damage formation mechanisms at a Si vertical wall by energetic incidence of hydrogen ions (H þ ) and other heavier ions are discussed based on molecular dynamics simulation. In typical plasma processing conditions, incident ions are highly directional toward the wafer surface and therefore ions that hit such a vertical wall do so only at nearly grazing angles. It has been found in this study that the penetration depth of H þ into a Si substrate is weakly dependent on the incident angle and therefore ions at grazing incidence can form deep damage. The results indicate that, in gate etching processes with HBr plasmas or other plasmas with hydrogen, control of energetic hydrogen ion bombardment is critical in minimizing possible surface damage at Si vertical walls. V

A gas cluster is a collection of atoms or molecules weakly bound by van der Waals forces. Gas clusters may form by the adiabatic expansion of gases. In this study, it is demonstrated by molecular dynamics simulations that a low-energy beam of oxygen gas clusters may be used to oxidize the top surface layer of silicon (Si) substrates without affecting its deeper layers. An incident oxygen gas cluster with sufficiently low incident energy may stick to the Si surface and expose a large number of oxygen molecules to the surface Si atoms for extended periods until the cluster sublimates. This may cause the formation of Si-O bonds only on the top Si surface. This is in contrast to the oxidation of Si by oxygen ion beams or plasmas, where deeper layers of the Si surface are typically oxidized by the energetic incident oxygen ions. An oxidized single Si layer may be chemically removed; therefore, this nearly single-layer oxidation process by oxygen gas cluster beams may lead to the development of a new atomic layer etching technology for Si.